8 Facts About Silver

Subtle silver gets pushed aside next to gold, but in many ways it outranks its lustrous competition. The cool-toned element is more conductive and more reflective, and boasts properties absent in other metals, like a reaction with light that put the “silver” in “silver screen.” Read on for more.

1. HUMAN USE OF SILVER DATES BACK TO 3000 BCE.

Archeological records show humans have mined and used silver (or Ag, number 47 on the periodic table) for at least 5000 years. Silver shows up in slag heaps at ancient mines in Turkey and Greece, as well as in deposits in China, Korea, Japan, and South America. Its visible shine made it popular in jewelry, decorative objects, and practical tools like the aptly named silverware. Its rarity gave it high value. Silver coins are credited with fueling the rise of classical Athens, and Vikings used “hacksilver”—chunks of silver bullion chopped off a larger block of the metal—as money.

2. SOME INDIGENOUS CULTURES WERE EXPERTS AT SILVERSMITHING.

As a soft, pliable metal, silver is easily smelted, but the process still requires moderate heat. Metal workers in the precolonial Americas didn’t have bellows to pump oxygen to a fire; instead, several people would encircle the fire and blow on it through tubes to increase its intensity. The Inca of the Andes became expert silversmiths. They believed gold was the sweat of the sun, and silver came from the tears of the moon.

3. SILVER CONDUCTS ELECTRICITY BETTER THAN ANY OTHER METAL.

Of all metals, silver is the best conductor of heat and electricity, so it can be used in a wide variety of applications. Metal solder, electrical parts, printed circuit boards, and batteries have all be made with silver. But it’s expensive: In electrical wiring, copper is often used instead.

4. ITS REACTIVITY TO LIGHT MADE EARLY PHOTOGRAPHY POSSIBLE.

In the 1720s, German physicist Johann Heinrich Schulze produced the first images with silver. Having discovered that a piece of chalk dipped in silver nitrate would turn black when exposed to sunlight, Schulze affixed stencils to a glass jar filled with a mix of chalk and silver nitrate. When he brought the jar into the sun, the light “printed” the stencil letters onto the chalk. A century later, Louis-Jacques-Mandé Daguerre created photographic prints on silver-coated copper plates. At the same time, British chemist William Henry Fox Talbot devised a method for developing an exposed image on silver iodide-coated paper with gallic acid.

“The effect was seen as magical, a devilish art. But this mystical development of an invisible picture was a simple reduction reaction,” science reporter Victoria Gill explains on the Royal Society of Chemistry’s podcastChemistry in its Element. “Hollywood could never have existed without the chemical reaction that gave celluloid film its ability to capture the stars and bring them to the aptly dubbed silver screen.” Silver salts are still used in rendering high-quality images.

5. THAT SAME REACTIVITY CAN ALSO CAUSE TARNISH.

Silver reacts with sulfur in the air, which forms a layer of tarnish that can darken or change the color of a silver object. The tarnish interferes with how silver reflects light, often turning the object black, gray, or a mix of purple, orange, and red. An at-home experiment can demonstrate the process: Put a shelled and quartered hard-boiled egg (preferably still warm) in the same container as a silver object, like a spoon, and seal the container closed. The tarnish should appear within an hour, thanks to the egg’s release of hydrogen sulfide gas, and grow darker as time goes on.

6. RESEARCHERS ARE STILL EXPLORING SILVER’S ANTIMICROBIAL PROPERTIES.

According to a 2009 review, silver was one of the most important anti-microbial tools in use before the discovery of modern antibiotics in the 1940s. The ancient Macedonians were likely the first to apply silver plates to surgical wounds, while doctors in World War I used silver to prevent infections when suturing battlefield injuries. Silver is toxic to bacteria, but not to humans—unless it’s consumed in large quantities. Ingesting too much silver can cause argyria, a condition where the skin permanently turns gray or blue due to silver’s reactivity with light.

A 2013 study in Science Transitional Medicine looked into the mechanisms behind silver’s anti-microbial powers. The findings suggested that silver makes bacterial cells more permeable and interferes with their metabolism. When antibiotics were administered with a small amount of silver, the drugs killed between 10 and 1000 times more bacteria than without it. “It’s not so much a silver bullet; more a silver spoon to help [bacteria] take their medicine,” lead researcher James Collins, a biomedical engineer at Boston University, told Nature.

7. SILVER IODIDE HELPS MAKE IT RAIN.

When regions need rain after a prolonged drought, scientists can “seed” clouds by spraying silver iodide particles into the atmosphere. In the 1940s, Bernard Vonnegut (brother of the author Kurt Vonnegut) demonstrated in a lab that silver iodide provides a scaffold on which water molecules can freeze, which (theoretically) would lead to precipitation in the form of snowflakes. In a 2018 study, researchers from the University of Colorado in Boulder and other institutions demonstrated the process in actual clouds. The team sent out two planes; one to spray silver iodide and the other to track its course and measure how water responded. The second plane recorded a zigzagged line of water particles freezing in the same flight path as the plane spraying silver, confirming silver iodide’s role in cloud seeding.

Bernard Vonnegut had made his discovery while he and his brother both worked for General Electric in Schenectady, New York. The two discussed the idea of water stabilized as ice at room temperature—a concept that Kurt Vonnegut went on to explore as ice-nine in his novel Cat’s Cradle.

8. SILVER IS RESPONSIBLE FOR A LOT OF GHOST TOWNS.

The United States established a “bimetallic” currency during George Washington’s presidency. The policy required the federal government to purchase millions of ounces of silver each year to mint coins or set the value of paper currency. Government demand for silver contributed to the boom of Western mining towns in the mid-19th century, encouraged by the 1890 Sherman Silver Purchase Act, which increased the federal purchase of silver.

But falling values in relation to gold eventually led to the repeal of the Sherman act, and the price of silver crashed. The mining settlements shrank from hundreds of residents to just a handful—and some were completely abandoned. Ghost towns (or minimally populated near-ghost towns) with names like Bullionville, El Dorado, Potosi, and Midas can still can be explored in Nevada, the Silver State.

10 Lustrous Facts About Gold

Gold’s symbol on the periodic table, Au, comes from its Latin name aurum, which means “glowing dawn.” This metal’s tantalizing yellow color and shining exterior has made gold a prized element in jewelry and treasured objects for thousands of years—but, amazingly, all of the gold that has ever been refined could melt down into a single cube measuring 70 feet per side. Read on for more opulent facts.

1. GOLD WAS PROBABLY THE FIRST METAL USED BY HUMANS.

Gold, number 79 on the periodic table, is almost twice as heavy as iron, but it’s incredibly malleable—and for that reason, it was probably the first metal humans ever wrought. The oldest known worked-gold artifacts, from the Thracian civilization in present-day Bulgaria, date back 4000 years; the death mask of the ancient Egyptian pharaoh Tutankhamun contains about 220 pounds of gold. Despite its presence in world cultures for millennia, “more than 90 percent of all of the gold ever used has been mined since 1848,” according to the American Museum of Natural History. That year marked the discovery of gold at Sutter’s Mill, California, launching the California Gold Rush.

2. ALL OF THE GOLD IN THE UNIVERSE MAY HAVE COME FROM COLLIDING NEUTRON STARS.

In 2017, astronomers from the University of California, Berkeley and other institutions observed two massive neutron stars spinning around one another at an accelerating rate. When the two stars—each with a mass up to twice that of our Sun—finally collided, gravitational waves rippled through the universe and clouds of neutron-rich material shot out. For the first time, researchers observed red light emanating from the collision, indicating the production of heavy metals like uranium, gold, and platinum. The finding supports the theory that all of the gold in the universe was formed this way—and that particles of that gold arrived on Earth in meteorites billions of years ago.

3. IT’S AN EXCELLENT CONDUCTOR OF ELECTRICITY.

Gold efficiently transfers heat and electricity—though not as well as copper and silver. In general, some metals conduct electricity well because their atoms share electrons easily: As electrical current flows, electrons move along in the same direction with just a little voltage. (The opposite would be true of insulators like glass, in which electrons move only when compelled to do so by thousands of volts of electricity.) Because gold resists oxidation and corrosion, it continues to move electrons even if occasionally exposed to the atmosphere. That’s why electrical contact surfaces are plated with a microscopic gold coating in smart phones, airbag sensor modules, and other devices.

4. YOU CAN FIND SUNKEN TREASURE, BUT YOU MIGHT NOT GET TO KEEP IT.

In 1985, Florida diver Mel Fisher located the Nuestra Señora de Atocha, a famed Spanish naval ship loaded with valuables that had sunk in a hurricane in 1622. Fisher’s motto was “finders, keepers”—and in the following decades, he retrieved gold, silver, emeralds, and pearls worth millions of dollars. Under admiralty law, Fisher was entitled to keep what he found, but archaeologists, historians, and conservationists protested. Two years after the discovery, Congress passed a law stating that riches found in wrecks within three miles of a U.S. coastline belong to the adjacent states.

5. GOLD CAN BE MEASURED WITH A UNIT FROM THE MIDDLE AGES …

The gold standard is a monetary system that ties a currency’s value to gold itself, which theoretically keeps inflation in check. The United States adopted this standard in 1879, but began to abandon the system in 1933 to stimulate the economy at the height of the Great Depression. The U.S. got rid of the gold standard entirely in 1971.

However, the U.S. Treasury still holds on to 261.5 million fine troy ounces of gold, using a unit of measurement that dates to the Middle Ages and is named after the city of Troyes, France. (A troy ounce is a few grams heavier than a regular ounce.) The goods are in the form of gold bullion (bulk gold shaped into bars), as well as coins and miscellaneous units, and stored in vaults at federal mints and reserve banks. As of September 2017, the government’s gold reserves total $335.5 billion in market value.

6. … OR IN BREAD.

Gold’s value has remained surprisingly steady over time. “King Nebuchadnezzar of Babylon, reigning in the 6th century BCE, bought 350 loaves of bread for an ounce of gold,” John Mulligan, head of member and market relations at the World Gold Council, tells Mental Floss. Roughly 2500 years later, with the current price of gold at about $1200 per ounce and a loaf of bread at $2.50, an ounce of gold would buy 480 loaves. “If we also then look at how gold compares with the historic purchasing power of the world’s major currencies over the last century or more,” Mulligan adds, “we see none of them has endured like gold.”

7. GOLD MIGHT HELP DESTROY CANCER.

“Gold just sits there and shines when it’s [in a] large [mass]—it doesn’t do much,” Mostafa A. El-Sayed, a leading chemist at the Georgia Institute of Technology, tells Mental Floss. “But when you cut it smaller and smaller, all of the sudden, it has different properties.” In a 2017 paper in Proceedings of the National Academy of Sciences, El-Sayed placed gold nanorods in mice with tumors and zapped the nanorods with a laser. The rods became hot enough to kill the adjacent cancer cells. Fifteen months later, the mice showed no long-term toxicity. In the paper on these findings, El-Sayed and his co-authors called this “a strong framework” for trying the technique in humans.

8. GOLD HAS BEEN USED IN DENTISTRY FOR AT LEAST 4000 YEARS.

Gold’s combined properties of malleability and biocompatibility (i.e., it can be tolerated inside the body) have made it useful in dentistry. Archaeologists have found gold dental modifications in skulls from Southeast Asia dating back 4000 years. The Bolinao skull, an artifact from the 14th or 15th century, is one of 67 skulls featuring decorated teeth that have been excavated in the Philippines. Ten-millimeter-wide gold plates are fixed in place on the incisors and canines in an overlapping fish-scale pattern. Today, gold-alloy crowns are still used to cap worn-down teeth or to strengthen weakened teeth.

9. NASA USES GOLD IN SPACE TECHNOLOGY.

The visors of astronauts’ space suits are coated with a layer of gold that’s just 0.000002 inches thick. The coating shields their eyes from the Sun’s harmful infrared light while allowing visible light in. That same ability to reflect infrared light will be put to work in the James Webb Space Telescope as it searches for light from the first stars and for potentially habitable exoplanets. The telescope will be equipped with 18 hexagonal mirrors in a honeycomb-like structure. Three grams of gold were vaporized in a vacuum chamber and then adhered to the telescope’s mirrors, which are made of beryllium. The layer of gold is just 100 nanometers thick—a tiny fraction of the thickness of a sheet of paper.

10. COLORADO’S CAPITOL BUILDING IS GILDED WITH PURE GOLD LEAF.

At least 10 state capitol buildings have gold-topped domes: Colorado, Connecticut, Georgia, Iowa, Massachusetts, New Hampshire, New Jersey, Vermont, West Virginia, and Wyoming. Colorado’s dome was restored in 2013 using about 65 ounces of pure gold that was mined in the state and hammered into leaves between one-8000th and one-10,000th of an inch thick. Gilders applied 140,000 3-inch squares of gold leaf to sticky copper plates that were then laid on the building’s dome. “The work is as much an art as a science due to how thin and fragile the gold leaf really is,” Doug Platt, communications manager for the state’s Department of Personnel and Administration, tells Mental Floss.

10 Facts About Silicon

How well do you know the periodic table? Our series The Elements explores the fundamental building blocks of the observable universe—and their relevance to your life—one by one.

Silicon is a metalloid: an element with properties not quite like a metal, nor exactly like a non-metal. If you have a cell phone in your pocket or dirt on your shoes, you’re carrying silicon. Learn more about this ever-present element.

1. IT'S JUST ABOUT EVERYWHERE.

It's the seventh most abundant element in the universe and even more prevalent in the Earth's crust, second only to oxygen as the most common element by weight. The layer under the crust—the mantle—is rich in silicon as well. With an atomic number of 14, it sits right below carbon on the periodic table.

2. SILICON ISN'T THE SAME THING AS SILICONE.

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The word silicone might make you think of breast implants, but it's actually a general term for a group of synthetic substances made of alternating silicon and oxygen atoms, with carbon and hydrogen molecules bonded on the sides. By mixing up these side groups of molecules and creating links between chains, chemists can create silicones with all sorts of different properties. Yes, you can find silicones in breast implants, but also in car polish, the insulation around electric cables, and even in your hair conditioner, where they help to calm down frizz. We can also thank silicones for Silly Putty, which was invented during World War II, when scientists were trying to create an alternative to rubber—and instead came up with a new national favorite toy.

3. WE USED SILICON FOR THOUSANDS OF YEARS WITHOUT KNOWING ITS ELEMENTAL NATURE.

Silica is the main ingredient of glass, which humans have been making at least since the Egyptians fashioned beads from the material in 2500 BCE. In China, the Qin and Han dynasties used purple and blue pigments made of barium copper silicates for various decorations, including parts of the famous terra-cotta army.

It took many centuries before people realized the substance could be further separated into two different elements—oxygen and silicon. In the late 1700s, French chemist Antoine Lavoisier noticed that certain materials classified as “earth” substances (which were dry and cold) sometimes behaved like metals (hard, dense, and resistant to being stretched, among other qualities). Silica was one of them. Perhaps, Lavoisier mused, some of the earths were really molecules of oxygen and a yet-undiscovered, metal-like element.

At the time, chemists didn’t know how to remove the oxygen atoms, which form strong bonds with the silicon atoms. That changed in the 1820s, when a Swedish chemist named Jons Berzelius finally managed to obtain silicon in his lab by purifying it from a silicon-containing compound. (Which one, and how he did it, isn't clear.) Berzelius's breakthrough came too late for Lavoisier, who had died in 1794, to see his speculations be proven true.

4. SILICA IS THE MOST COMMON FORM OF SILICON.

Also known as silicon dioxide, this molecule is composed of one silicon atom and two oxygen atoms (SiO2). Most of what we call silicon is actually silica, found in both minerals and plants. Many plants create unique microscopic structures called phytoliths using silica they take up from the soil. Scientists aren't sure why: They might offer protection against microscopic harm or provide structural support, or maybe they're just a way for a plant to use up extra silica.

Phytoliths stick around long after a plant decays, which can illuminate the deep history of an area—whether it used to be a forest or grassland, for instance, or how people used the landscape. Dan Cabanes, a phytolith expert and anthropologist at Rutgers University, has used phytoliths to understand how Neanderthals made a home in a cave in northern Spain, creating a sleeping area with grass bedding they used repeatedly. And because phytoliths survive burning, “we can study how they made fire or what type of food they were consuming,” Cabanes tells Mental Floss.

The picture isn’t always perfect, though, because sometimes two different plants make phytoliths of the same shape—and some plants don’t make them at all.

5. IT'S A KEY COMPONENT OF SOME BEAUTIFUL STONES …

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Gorgeous gemstones like amethyst, onyx, and agate are all made of silica. In each rock, the silica molecules are arranged in repeating 3D geometries called crystal structures. Different arrangements, as well as small impurities in the rock, give each gemstone its unique appearance.

6. … AND THE DAZZLING BEAUTY OF DIATOMS.

Silica also forms the cell walls of diatoms, a type of algae found all over the world. Diatoms, which come in a mesmerizing variety of shapes, can live in both fresh and saltwater. When they die, their cell walls can accumulate into chalky deposits of "diatomaceous earth," which we use in all sorts of things, from cat litter to toothpaste.

7. SILICON IS VERY USEFUL IN TECH …

Silicon can act as a semiconductor—a material that neither conducts electricity perfectly nor insulates against it, but rather lies somewhere in between. This property is important in many parts of electronics, where you want some control over the flow of electricity. “What's beautiful about semiconductors is that you can tune their conductivity by adding impurities,” Eric Pop, a professor of electrical engineering at Stanford University, tells Mental Floss. Pure silicon is an insulator, but if you ‘dope’ it with tiny amounts of certain other elements, such as phosphorus or arsenic, it becomes better at conducting electricity.

Other materials, including germanium or gallium arsenide, are better semiconductors than silicon, but silicon is the most popular choice among electronics manufacturers (whose concentration south of San Francisco in the 1970s inspired the name "Silicon Valley"). It's cheap, it’s everywhere, and because it likes to oxidize so much, it can conveniently create its own insulating layer when exposed to air.

8. … BUT RESEARCHERS WANT TO FIND BETTER OPTIONS.

Engineers like Pop are looking for materials to replace silicon in our electronics to help keep up with the demand for faster computing. “Silicon is sort of like the Honda Civic of semiconductors,” Pop says. “It gets the job done, but it’s not very fast.” However, Pop thinks that even when pitted against superior materials, silicon won’t completely disappear, thanks to its low cost.

9. SILICON HOLDS UP MANY OF OUR BUILDINGS.

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Many common building materials are based on silicon-containing substances. Clay minerals, which contain silicon, are used to make bricks, as well as Portland cement, which is then used as the binding agent in concrete.

10. AMERICANS LEFT A BIT OF SILICON ON THE MOON.

When Buzz Aldrin and Neil Armstrong became the first humans to walk on the Moon, in 1969, they left a few things on its surface besides their footprints. One was a small silicon disc, inscribed with messages from the leaders of 73 countries, from Afghanistan to Zambia. The disc is housed inside a protective aluminum case and is stashed in a small bag along with a few other items. Silicon was elected official message-bearer because it could endure the huge range of temperatures on the Moon. The disc nearly didn’t make it, though: Aldrin had forgotten all about the bag, tucked into a pocket of his space suit sleeve, and he was already on the ladder to the spacecraft when Armstrong reminded him about it. Aldrin tossed the pouch onto the Moon.